1. Field
This patent specification relates to the field of IC sockets used primarily for electrical measurements of semiconductor devices and, in particular, to IC sockets suitably used for measurements of devices such as a wafer level chip size package provided with a plurality of minute external contact terminals.
2. Discussion of the Background
IC sockets are widely used for achieving electrical connections between external connecting terminals of semiconductor devices and measurement apparatuses, and for carrying out electrical measurements of characteristics of devices such as CSP (chip size package), for example. An IC socket is provided with a plurality of connecting terminals at the location corresponding to a plurality of external connection terminals of the semiconductor device such that an electrical connection can be achieved between these corresponding terminals.
Regarding the electrical measurements of characteristics of semiconductor devices, there generally exists some resistance at the portions where the IC socket is in contact with the semiconductor device (current-carrying portion), in which the resistance depends largely on contact pressure between the terminals under contact. It is desirable for the IC socket to have a contact resistance that is as small as possible, or infinitesimally close to zero.
In addition, the contact resistance is preferably stable throughout the measurements under current-carrying conditions so that the measurements on current, resistivity, capacitance and etc, and operation check in general, can be carried out satisfactorily without any retardation.
In previously known IC sockets, stable contact between an IC socket with external connection terminals of semiconductor devices is implemented by forming contacts utilizing an elastic body such as a spiral spring or resinous material.
For example, a semiconductor device is placed in an IC socket by using an elastic body such as a spiral spring or resinous material to press against one of the faces of the device opposite to external connection terminals such that the external connection terminals come into contact with the contacting terminals of the IC socket. (For example, Japanese Laid-Open Patent Applications No. 11-135217 and 2000-133397.)
Of particular concern is a wafer level CSP, which has external connection terminals prefabricated therein prior to dicing steps (for example, Japanese Laid-Open Patent Application No. 2000-260910).
The wafer level CSP has in general an outer size of approximately 1 mm square and 0.4 mm thick and is provided with external connection terminals each having a diameter of about 0.2 mm.
As described above, in order to stabilize the contact between the IC socket with external connection terminals of a semiconductor device, one of the faces of the device opposite to external connection terminals is pressed against contacting terminals of the IC socket by means of an elastic body such as a spiral spring or resinous material. Using this method, however, delicate control of pressurizing forces is difficult to achieve.
As a result, when the measurements are made on minute devices such as a wafer level CSP, in particular, difficulties may arise in the previous methods in which adverse effects may take place such as the damage of external connection terminals of the device and cracking and/or fracturing in chips.